Process for purification of crude 4,4'-diamino-1,1'-dianthraquinonyl-3,3'-disulfonic acids and salts thereof

Abstract

Crude 4,4'-diamino-l,l'-dianthraquinonyl-3,3'-disulfonic acids or salts thereof are purified by subjecting an aqueous solution containing the crude products to salting-out using inorganic salts, the aqueous solution being adjusted within a range of from acid to neutral region, whereby a product usable as such for the production of 4,4'-diamino-1,1'-dianthraquinonyl red pigments having excellent pigmentary properties is obtained in high yields with industrial advantages.

We claim: 
     
       1. A process for preparation of disulfonic acid intermediates of 4,4'-diamino-1,1'-dianthraquinonyl red pigments from a crude 4,4'-diamino-1,1'-dianthraquinonyl-3,3'-disulfonic acid or salt thereof, which comprises mixing an inorganic salt with an aqueous solution containing the crude disulphonic acid or the salt thereof to effect salting-out, the aqueous solution being adjusted to an acidic pH after or before the mixing. 
     
     
       2. The process according to claim 1, wherein the inorganic salt is used in an amount of about 1 to 5% by weight based on the weight of the aqueous solution. 
     
     
       3. The process according to claim 1, wherein the inorganic salt is selected from alkali metal salts and alkaline earth metal salts. 
     
     
       4. The process according to claim 1, wherein the inorganic salt is selected from sodium chloride, sodium sulfate and a mixture thereof. 
     
     
       5. The process according to claim 1, wherein concentration of the 4,4'-diamino-1,1'-dianthraquinonyl-3,3'-disulfonic acid or the salt thereof in the aqueous solution ranges from about 4 to 7% by weight based on the weight of the aqueous solution. 
     
     
       6. The process according to claim 1, wherein the mixing of the inorganic salt with the aqueous solution is carried out at a temperature of 70° to 100° C. 
     
     
       7. The process according to claim 1, wherein the aqueous solution is adjusted to a pH ranging from about 1 to 5 after or before the mixing. 
     
     
       8. The process according to claim 1, wherein the aqueous solution is adjusted to a pH ranging from about 1 to 5, and then the mixing of the inorganic salt with the aqueous solution is carried out. 
     
     
       9. The process according to claim 1, wherein the mixing of the inorganic salt with the aqueous solution is carried out at a temperature of 70° to 100° C., and then the mixture is kept at a temperature of 20° to 60° C. to effect the salting-out. 
     
     
       10. The process according to claim 1, wherein the aqueous solution is prepared by allowing a 1-amino-4-halogenoanthraquinone-2-sulfonic acid or a salt thereof to react in the presence of metallic copper or a copper compound in an acidic medium under heating, making the reaction mixture alkaline and then subjecting the resulting reaction mixture to hot-filtration, whereby the aqueous solution is obtained as a filtrate. 
     
     
       11. A process for producing a 4,4'-diamino1,1'-dianthraquinonyl-3,3'-disulfonic acid or a salt thereof, which comprises preparing an aqueous solution containing a crude 4,4'-diamino-1,1'-dianthraquinonyl-3,3'-disulfonic acid or a salt thereof, and mixing an inorganic salt with the aqueous solution to effect salting-out, the aqueous solution being adjusted to an acidic PH after or before the mixing of the inorganic salt with the aqueous solution, whereby a 4,4'-diamino-1,1'-dianthraquinonyl-3,3'-disulfonic acid or a salt thereof useful as such for production of a 4,4'-diamino-1,1'-dianthraquinonyl red pigment is produced. 
     
     
       12. The process according to claim 11, wherein the aqueous solution containing a crude 4,4'-diamino-1,1'-dianthraquinonyl-3,3'-disulfonic acid or a salt thereof is prepared by allowing a 1-amino-4-halogenoanthraquinone-2-sulfonic acid or a salt thereof to react in the presence of metallic copper or a copper compound in an acidic medium under heating, making the reaction mixture alkaline, and subjecting the resulting reaction mixture to hot-filtration to remove a copper compound formed during the reaction.